Doctors have discovered how oily fish protects against heart disease and stroke.

Researchers at Southampton University have found that omega-3 oils stop the build up of fatty deposits in the arteries.

If left unchecked these deposits can block key routes to the heart or brain triggering an attack or stroke.

It reinforces advice to eat one portion of white fish and one portion of oily fish every week

Sir Charles George, British Heart Foundation

The findings add to growing evidence that eating oily fish or taking fish oil supplements reduce the risks of this happening.

Professor Philip Calder and colleagues based their findings on a study of 162 patients who were waiting to have surgery to remove dangerously high levels of fatty build-up or plaques in their arteries.

Daily supplements

The patients were divided into three groups and were asked to take either omega-3 fish-oil capsules, sunflower-oil capsules or a dummy capsule six times a day. On average, they took the capsules for 42 days.

After the patients underwent surgery, doctors examined their plaques.

They found that there were far fewer inflammatory cells in the plaques of patients who had taken the omega-3 fish oil capsules.

This meant that they were less likely to rupture and to trigger a heart attack or stroke.

Professor Calder hailed the results saying they offered hope to the hundreds of thousands of people who die from arterial disease every year.

He suggested that people should eat more oily fish or take fish-oil supplements.

"I have no hesitation in recommending that people increase their consumption of omega-3s, even if they are not ill, because they are protective," he said.

"Increasing their intake of omega-3 fatty acids simply by eating more oily
fish or taking fish oil capsules can reduce their risk of heart-related death."

Professor Calder acknowledged that the patients involved in the study took relatively high doses of omega-3 oil.

However, he suggested that taking much lower amounts over longer periods could be equally beneficial.

"We gave them about 1.6 grams of omega-3 per day, which is 10 times more than people would normally have," he said.

"To achieve this level people would have to consume several oily fish meals a
week or take quite a number of fish oil capsules per day.

"The level we're talking about is quite high, but if people have a very long
period of exposure to a lower dose it might have the same effect."

More research

The Stroke Association welcomed the study but said more research is needed to determine how much omega-3 oils people should take.

Eoin Redahan, one of its directors, said: "This research strengthens the information that has already been around about omega-3 fatty acids."

But speaking to BBC News Online, he added: "What we don't know is how much omega-3 should be taken and how it should be taken.

"For instance, if you take too much it can block the normal blood clotting process and that in turn could lead to excessive bleeding. This could be dangerous after someone has suffered a haemorrhagic stroke."

Professor Sir Charles George, Medical Director at the British Heart Foundation, added: "This research is important, and it reinforces advice to eat one portion of white fish and one portion of oily fish every week."